In a conventional image forming device, a developer is supplied from an image forming device to, and fixed on, a recording medium through an exposure process, a development process, a transfer process and a fusion process. The developer (hereinafter referred to as “toner”) used the image forming device is generally produced by adjusting a molecular weight of toner mother particles composed of colorant, resin, wax and charge control agent and by adding an external additive to the toner mother particles. Of this type of toner, there is toner that suppresses occurrence of fogging (smear) in which toner is attached to non-printed areas of the recording medium by making a charging polarity of a part of the external additive reversed from a charging polarity of the toner mother particles (see, for example, Japanese Laid-Open Patent Application No. 2003-295500, paragraphs 0037-0048 and FIG. 1).